There has been proposed a composite material of ceramics having a matrix reinforced by dispersing carbon fibers or fibers or whiskers of ceramics such as silicon carbide in granular matrices of ceramic materials having a high melting point such as alumina, zirconia or the like and thereafter sintering these granular matrices at a high temperature (refer to "Ceramics" issued by Yogyo Kyokai, 22(1987) No.6).
As a method of producing these conventional ceramics composite materials, it has been a general practice to employ ceramics powder as a raw matrix material, mechanically mixing this powder with fibers or whiskers of ceramics in a ball mill or the like, and thereafter sintering the mixture.
When the raw material is thus prepared from ceramics powder, however, it is impossible to sufficiently fill up clearances or interstices between the fibers or whiskers of ceramics with the ceramics powder even by mechanical mixing as the content of the fibers or whiskers of ceramics is increased. As a result, a sufficiently dense sintered body cannot be obtained by sintering, and hence it has been impossible to obtain a satisfactory characteristic such as mechanical strength. Further, mechanical mixing has caused damage and breakage of the fibers or whiskers of ceramics.
Since it is not easy to homogeneously disperse the reinforcement material in the ceramics powder as hereinabove described, the employable reinforcement has been restricted to short fibers or whiskers of ceramics. However, short fibers and whiskers localize any energy dispersion against external loads. Thus, it has been impossible to sufficiently make the best use of the high strength characteristic provided by a mixed reinforcement material, while not much of any characteristic improvement has been attained even if compounding was performed.
On the other hand, there has been studied a method of adhering matrix materials of ceramics to fibers or whiskers of ceramics for serving as the reinforcement, by a CVD process or impregnating the fibers or whiskers in a slurry of ceramics for serving as the matrix and thereafter sintering the same. However, it has been impossible to sufficiently fill up clearances or interstices between the fibers or whiskers, with the matrix material in the CVD process. Further, the method of impregnating the fibers in a slurry has such a disadvantage that moisture etc. contained in the slurry evaporates or volatilizes during the sintering thereby reducing solid residues, thereby easily causing pores in the sintered product.
Thus, in compounding of the matrix material and the reinforcement material, densification of the composite material is difficult as the content of the reinforcement material is increased, and hence the content of the reinforcement has generally remained at 15 to 20 volume percent and 30 volume percent at the most. Accordingly, it has been difficult to obtain a ceramics composite material which is dense and has excellent characteristics such as strength, toughness and the like.
In order to efficiently obtain a machine part such as an engine part or the like through use of such a ceramics composite material, further, a technique is required for forming the same into a desired configuration.
However, since ceramics powder has been employed as a raw matrix material in the conventional forming method, a sintering process is necessarily required similarly to the case of obtaining general ceramics. Further, it has been impossible to use a sintering method at atmospheric pressure since fibers or whiskers of ceramics introduced as the reinforcement material prevent densification of the sintered body.
An attempt has been made for forming a mixture obtained by mixing ceramics powder serving as the raw matrix material and fibers or whiskers of ceramics serving as the reinforcement material, with a mechanical press and sintering the same by hot pressing or the like ("FC Report" issued by Shadan Hojin Nippon Fine Ceramics Kyokai, Vol. 4(1986) No. 6, for example).
Therefore, it has barely been possible to obtain a mere simple configuration such as a plate-type or pole-type one. In order to obtain a configuration of an engine part or the like, for example, it is necessary to cut a portion of a certain configuration from a composite material compact having a simple configuration and finish the same to the final configuration through a step such as grinding with a diamond grindstone or the like. Such operational steps for obtaining the final configuration of the engine part or the like are very costly and constitute a hindrance to the widespread use of ceramics composite materials.